Material to prevent Zika infection by mosquitoes are displayed at the 69th World Health Assembly at the United Nations European headquarters in Geneva, Switzerland, May 23, 2016. Photo: Reuters/Denis Balibouse

U.S. health officials are investigating the mysterious case of a person in Utah who contracted Zika while caring for an elderly man infected with the virus who died last month.

Federal and state health officials said on Monday it is not clear how the individual contracted Zika, a virus that is most typically transmitted by the bite of an infected mosquito and occasionally through sex with an infected person.

The person had not traveled to an area with active Zika transmission nor had sex with a person who had recently returned from such a place. Health officials say they are not aware of any mosquitoes in Utah that are capable of transmitting the virus.

“The new case in Utah is a surprise, showing that we still have more to learn about Zika,” said Dr. Erin Staples, CDC's medical epidemiologist who is in Utah leading an investigation into how the infection occurred.

“Fortunately, the patient recovered quickly, and from what we have seen with more than 1,300 travel-associated cases of Zika in the continental United States and Hawaii, non-sexual spread from one person to another does not appear to be common.”

Experts outside the CDC say the most likely possibility is that the person came into contact with blood or urine or other bodily fluids while caring for the infected person.

"We are still doing a lot of investigation to understand whether Zika can be spread person-to-person through contact with a sick person," said Dr. Satish Pillai of the CDC, who is investigating the case.

Gary Edwards, director of the Salt Lake County Health Department, said the infected individual is a family contact of the man who died.

The cause of the deceased person's death is still under investigation, but the man was infected with Zika at the time of death and officials believe the virus was a contributing factor. He contracted Zika on a trip to a country with active transmission.

"We know that the patient had contact with the deceased patient while the deceased patient was very ill. The exact nature of that contact, we are still investigating," Edwards said.

CDC tests showed extremely high levels of virus in the deceased man's blood, which were more than 100,000 times higher than seen in other samples of infected people.

"This is a very unique situation with these elevated viral loads that we haven't previously seen," Pillai told reporters in a telephone briefing.

Dr. Michael Bell, a CDC medical epidemiologist, said it was not clear whether the man's underlying condition had diminished his immune system, allowing the virus to replicate unchecked, or if the virus simply overpowered his immune system.

Bell said CDC is taking the high viral load issue very seriously, but said it is "too early to make a clear statement about what we think could have happened."

Dr. Amesh Adalja, a spokesman for the Infectious Diseases Society of America, said it will be important to know whether the family contact of the deceased man had any skin lacerations or skin disease that might have allowed the virus access to the patient's blood.

"We know bodily fluids like saliva and urine can harbor the virus, he said.

Health officials are also investigating whether mosquitoes might have played a role.

Tom Hudachko, director of communications for the Utah Department of Health, said state officials are not aware of any mosquitoes known to carry the Zika virus within Utah. He said there were a few Aedes aegypti mosquitoes - the kind that carry Zika - discovered in traps in the southwestern parts of the state several years ago, but there have not been any since.

Utah does not have any Aedes albopictus mosquitoes, the other type that has been found capable of transmitting Zika. Health officials are doing mosquito trapping and testing near the deceased patient's home "to make sure this is not a potential route of transmission," Hudachko said.

As of July 13, 2016, 1,306 cases of Zika have been reported in the continental United States and Hawaii; none of these have been the result of local spread by mosquitoes. Of these, 14 are believed to be the result of sexual transmission and one was the result of laboratory exposure.